METHOD FOR SCHEDULING VoIP TRAFFIC FLOWS

ABSTRACT

The present invention relates to a method for scheduling a data transmission to a user equipment in a communication system comprising at least one radio network controller (RNC) governing a number of base stations, wherein the communication system supports data transmission from a base station to an user equipment on a high speed packet access (HSPA) bearer or a dedicated channel (DHC) or on similar bearers in a CDMA2000 system. The method comprises the steps of: identifying at least one predetermined scheduling condition for data transmissions for the user equipment; determining at least one current scheduling conditions of the user equipment; comparing the predetermined scheduling conditions of the user equipment with the current conditions of the user equipment; selecting a bearer for the data transmissions during a session from a base station based on the comparison; and using the selected data bearer during the data transmission session or until a new data bearer has been selected. Furthermore, the invention relates to a user equipment, a radio network controller, a computer readable medium and mobile communication system for data transmissions such as VoIP service transmissions in wireless communications systems

TECHNICAL FIELD

The present invention relates in general to the field of communications,and, in particular, to communication systems where a user of a firstuser equipment is able to communicate with a second user using, forexample, a second user equipment or a PSTN phone using a VoIP service,such as a MMTel (Multimedia Telephony) service, PoC service or a PoC VGM(Video Group Message), provided by an application server, e.g. a SIPapplication server (Session Initiation Protocol application server).

BACKGROUND OF THE INVENTION

As wireless communication systems evolve, there is an increasing need toaccommodate wireless communications systems that not only convey (i.e.transmit and/or receive) voice but also allow data information to beconveyed between users of the communication system. The data informationis various types of digital information such as text, graphics and otherdigital information that are typically not time sensitive. Informationsuch as voice or video are time sensitive in that once transmission hascommenced there can be no appreciable delay in subsequent transmissions.Any appreciable delay in consecutive transmissions of the time sensitiveinformation causes annoying interruption or causes the information to beunintelligible to a receiving user equipment (UE), e.g. cellulartelephones, pagers and wireless computers. Data information, on theother hand, can tolerate delays in consecutive transmissions and thuscan be processed differently from time sensitive signals.

High Speed Packet Access (HSPA) and mainly High Speed Downlink PacketAccess (HSDPA) has emerged as interesting alternative to traditionaldedicated channels (DHC) when Voice over Internet Protocol (VoIP) is tobecome implemented on a wide basis. VoIP is the routing of voiceconversations over the Internet or any other IP-based network. The voicedata flows over a general-purpose packet-switched network, instead oftraditional dedicated, circuit switched voice transmissions lines.Wireless communication systems such as the HSDPA specification in theUniversal Mobile Telecommunication System (UMTS) standard canaccommodate the conveyance of data information hereinafter referred towireless data system. A protocol is generally a set of rules thatdictate how communication is to be initiated, maintained and terminatedbetween system equipment and/or user equipment of the communicationsystem. The wireless data systems are structured in substantially thesame manner as other wireless communication systems in that theycomprise a plurality of base stations located in cells. A cell is ageographical area defined by physical boundaries. Each cell has basestation equipment (or cell site) that services user equipment (UE)located in that cell. The UE is being serviced with appropriate amountsof various resources (e.g. power, bandwidth) to enable the UE to conveyadequately information to other users or other system equipment. Basestation equipment is generally system equipment comprising communicationequipment (e.g. radio transmitters, receivers, processing equipment)owned, controlled and operated by system providers.

A UE receives information from a base station equipment over a downlinkand transmits information to a base station equipment over an uplink.The uplink comprises at least one traffic channel and at least onesignalling channel. Similarly, the downlink comprises at least onesignalling channel and at least one traffic channel. The traffic channelis a communication channel over which user information or trafficinformation (e.g. voice, video, data) is conveyed between UEs and systemequipment of the communication system. The signalling channels arecommunication channels used by the system to manage, and otherwisecontrol the operation of communication channels of the communicationsystem.

Investigations have shown that the system capacity can be significantlyincreased with HSPA in comparison to DCH. However, a problem with HSDPAis that it does not support soft handover. Soft handover has beenintroduced in the CDMA digital cellular standard. Due to the propertiesof the CDMA signalling scheme, it is possible for a CDMA subscriberstation, i.e. a UE, to simultaneously receive signals from two or morebase stations that are transmitting the same bit stream on the samechannel. If the signal power from two or more base stations is nearlythe same, the UE may combine the received signals in such a way the bitstream is decoded in a more reliable way than if only one base stationwere transmitting. If any one of these signals fades significantly,there will be a relatively high probability of having adequate signalstrength from one of the other base stations. Furthermore, during ahandover between base stations all data buffered in old base stations islost. This in contrast to DHC bearers, which support soft handovers thatdo not lead to packet loss. The effect of packet loss is that handoversbetween cells is experienced as interruptions in the speechcommunication. The interruptions can be as long as 160 ms or evenlonger. If the handovers occur frequently, this may be very annoying andmay, hence, have an negative impact on the perceived interactivity inthe user communications.

A solution to this problem, i.e. to reduce the impact of the HSDPAhandover on speech quality, may be to reduce the amount of data bufferedin the base station. However, this can only be perform to a limitedextent since some buffering in the base station always is needed inorder to benefit from the high available bit rates when utilizing HSPA.

Thus, there is a need for an improved method that provides for areduction of the impact of the handover on speech quality in wirelessdata networks supporting HSDPA, such as UMTS (WCDMA), and in wirelessdata networks such as CDMA2000, hence, enhances the perceivedinteractivity in user communications.

BRIEF DESCRIPTION OF THE INVENTION

An object of the present invention is to provide an improved method, aradio network controller, a user equipment and mobile communicationsystem that reduce the impact of the handover on speech quality inwireless data networks such as CDMA 2000 and in systems supportingHSDPA, such as UMTS (WCDMA), and, hence, enhance the perceivedinteractivity in user communications.

Another object of the present invention is to provide an improvedscheduling handling in wireless data networks such as CDMA2000, and inwireless data networks supporting HSDPA, such as UMTS (WCDMA) to enhanceperceived interactivity in user communications.

A further object of the invention is to provide a method, a radionetwork controller, a user equipment and mobile communication systemthat minimize the negative impact from interruptions in the data trafficduring data transmissions such as VoIP service transmissions caused bypacket loss at handovers in wireless communications systems supportingHSDPA, for example, WCDMA networks, and in wireless data networks suchas CDMA 2000.

Yet another object of the present invention is to provide a method, aradio network controller, a user equipment and mobile communicationsystem for data transmissions such as VoIP service transmissions inwireless communications systems in wireless data networks such as CDMA2000 and in systems supporting HSDPA, such as UMTS (WCDMA), that keepthe system capacity as high as possible with minimal negative impactfrom handover interruptions for high mobility users.

Another object of the present invention is to provide method, a radionetwork controller, an user equipment and a mobile communication systemthat reduce the impact of the handover on speech quality in wirelessdata networks such as CDMA2000 using HDR (High Data Rate) and, hence,enhances the perceived interactivity in user communications. A HDRsystem is optimized for packet data services, with a flexiblearchitecture based on IP protocols. HDR can overlay an existing wirelessnetwork or work as a stand-alone system. HDR, known as TIA/EIA/IS-856“CDMA2000, High Rate Packet Data Air Interface Specification” is alsoknown as 1×EV.

At least some of these objects and other objects are achieved accordingto the present invention by a method, a radio network controller, andmobile communication system having the features defined in theindependent claims. Preferred embodiments are defined in the dependentclaims.

In the context of the present invention, the term “VoIP services”relates to services that provide audio using the IP protocol fortransport the media. Example services are MMTel (MultiMedia Telephony)services, Push to talk over Cellular (PoC), or VoIP with video and/orimages and services related to music. Moreover, the term “applicationserver” relates to a server handling such services.

According to a first aspect of the invention, there is provided a methodfor scheduling data transmission to a user equipment in a communicationsystem comprising at least one radio network controller (RNC) governinga number of base stations, wherein the communication system supportsdata transmission from a base station to an user equipment on a highspeed packet access (HSPA) bearer or a dedicated channel (DHC) or onsimilar or corresponding bearers in a CDMA2000 system. The methodcomprises the steps of identifying predetermined scheduling conditionsfor data transmissions for the user equipment; determining currentscheduling conditions of the user equipment; comparing the predeterminedscheduling conditions of the user equipment with the current conditionsof the user equipment; selecting a high speed packet access (HSPA)bearer or a dedicated channel (DHC) or similar bearers in a CDMA2000system for the data transmissions during a session from a base stationbased on the comparison; and using the selected data bearer during thedata transmission session or until a new data bearer has been selected.

According to a second aspect of the present invention, there is provideda radio network controller (RNC) in a communication system governing anumber of base stations, wherein the communication system supports datatransmission from a base station to an user equipment on a high speedpacket access (HSPA) bearer or a dedicated channel (DHC) or on similaror corresponding bearers in a CDMA2000 system, the RNC being adapted toschedule data transmissions to a user equipment. The controllercomprises: identifying means adapted to identify at least onepredetermined scheduling condition for data transmissions for the userequipment; determining means adapted to determine at least one currentscheduling condition of the user equipment; comparator means adapted tocompare the predetermined scheduling conditions of the user equipmentwith the current conditions of the user equipment; scheduling selectingmeans adapted to select a high speed packet access (HSPA) bearer or adedicated channel (DHC) or similar bearers in a CDMA2000 system for thedata transmissions during a session from a base station based on thecomparison, wherein the selected data bearer is used during the datatransmission session or until a new data bearer has been selected.

According to a third aspect of the present invention, there is provideda mobile communication system comprising at least one radio networkcontroller (RNC) governing a number of base stations, wherein thecommunication system supports data transmission from a base station toan user equipment on a high speed packet access (HSPA) bearer or adedicated channel (DHC) or on similar or corresponding bearers in aCDMA2000 system, the RNC being adapted to schedule a user equipment in adata transmission in the network. The controller is adapted to identifyat least one predetermined scheduling condition for data transmissionsfor the user equipment; determine at least one current schedulingconditions of the user equipment; compare the predetermined schedulingconditions of the user equipment with the current conditions of the userequipment; select a high speed packet access (HSPA) bearer or adedicated channel (DHC) or similar bearers in a CDMA2000 system for thedata transmissions during a session from a base station based on thecomparison; and use the selected data bearer during the datatransmission session or until a new data bearer has been selected.

According to fourth aspect of the present invention, there is provided auser equipment for use in a communication system comprising at least oneradio network controller (RNC) governing a number of base stations,wherein the communication system supports data transmission from a basestation to an user equipment on a high speed packet access (HSPA) beareror a dedicated channel (DHC) or on similar or corresponding bearers in aCDMA2000 system. The user equipment comprises identifying means adaptedto identify at least one predetermined scheduling condition for datatransmissions; determining means adapted to determine at least onecurrent scheduling condition of the user equipment; comparing meansadapted to compare the predetermined scheduling conditions of the userequipment with the current conditions of the user equipment; and meansfor communicating the comparison to the RNC.

According to fifth aspect of the present invention, there is provided auser equipment for use in a communication system comprising at least oneradio network controller (RNC) governing a number of base stations,wherein the communication system supports data transmission from a basestation to an user equipment on a high speed packet access (HSPA) beareror a dedicated channel (DHC) or on similar or corresponding bearers in aCDMA2000 system. The user equipment comprises determining means adaptedto determine at least one current scheduling condition of the userequipment; and means for communicating the at least one currentscheduling condition of the user equipment to the RNC.

According to a further aspect of the invention there is provided acomputer readable medium comprising instructions for bringing aprogrammable device to perform steps of the method according to thefirst aspect of the invention.

The present invention is hence based on the idea of actively selecting aHSPA data bearer or a dedicated channel (DHC) for a data transmission ora similar or corresponding data bearer in a CDMA2000 system, e.g. a VoIPservice data transmission, to a user equipment based on a comparisonbetween at least one predetermined scheduling condition and currentscheduling conditions, which conditions may include type of trafficflow, mobility of user equipment, system load, etc. In other words, ascheduling decision is made for a specific user equipment on basis ofthe comparison. Thereby, there is possible to select a data bearer thatminimizes the risk for undesired interruptions during data transmission,such as VoIP service data transmissions, and, thus, the perceivedinteractivity in user communications can be enhanced at the same time assystem capacity is maximized.

According to an embodiment, the at least one predetermined schedulingcondition is a predetermined mobility threshold of the user equipmentand the step of determining the current scheduling conditions of theuser equipment comprises the step of determining the mobility of theuser equipment. A HSDPA bearer is selected if an current mobility of theuser equipment is determined to be below the threshold and a DCH beareris selected if the current mobility is determined to be above thethreshold. Thereby, it is possible to select data bearer on basis of themobility of a specific user. The threshold can be set such that a givennumber of users (or sessions) are scheduled to use DCH bearers if theirmobility is high. The threshold can, for example, be set for a specificuser equipment or for a group of users. As the number of DCH users iskept controlled by means of the threshold, the system capacity can bekept as high as possible with a minimal negative impact from handoverinterruptions for high mobility users which are scheduled to HSPAbearers.

Upon setting the threshold, the insight that the probability density ofmobile users in a system is distributed such that there is a highdensity at relatively low mobilities, e.g. users that are walking or arein an office, and a high density at relatively high mobilities, e.g.user who are travelling by car or by train, is used. That is, thethreshold can be set such that users with a relatively low mobility arescheduled to a HSDPA bearer and user who are travelling by car or bytrain are scheduled to a DCH bearer. User who are travelling at a lowvelocity, i.e. walking, will experience a low handover frequency andwill thus not encounter interruptions especially often. On the otherhand, user with a high mobility are scheduled to the less capacityefficient DCH bearers. These user would otherwise, if they werescheduled to a HSDPA bearer, experience handover quite often, which maybe very annoying. Hence, a high degree of perceived interactivity inuser communications can be obtained for high mobility users at the sametime as system capacity can be kept as high as possible.

In a further embodiment of the present invention, the predeterminedmobility threshold is an adjustable mobility threshold. The thresholdfor a specific user or for a group of users can be changed or adjusteddepending of the system load and/or operator preferences. If forinstance the system load is very high it may be desirable to move thethreshold to a high value, i.e. to a high mobility, in order to maximizesystem capacity. As the numbers of DCH users is kept controlled by meansof the adjustable threshold, the system capacity is kept as high aspossible with minimal negative impact from handover interruptions forhigh mobility users.

According to a further embodiment of the present invention, the currentscheduling conditions of the user equipment are continuously checkedduring the session in order to identify whether the current conditionshas changed and if the conditions has changed and the updated conditionsis compared with the predetermined scheduling conditions. If thecomparison between the updated conditions and the predeterminedscheduling conditions indicates that the selected data bearer should bechanged; a new data bearer for the data transmissions is selected basedon the comparison between the updated conditions with the predeterminedscheduling conditions. Consequently, the allocation of data bearer isdynamic, that is the scheduling (i.e. the selection of a HSDPA or a DCHbearer) is performed during the session by continuously monitoring thecurrent scheduling conditions i.e. the current mobility of the user.Thereby, it is possible to account for the current load in the visitedcell.

As realized by the person skilled in the art, the methods of the presentinvention, as well as preferred embodiments thereof, are suitable torealize as a computer program or a computer readable medium.

The features that characterize the invention, both as to organizationand to method of operation, together with further objects and advantagesthereof, will be better understood from the following description usedin conjunction with the accompanying drawings. It is to be expresslyunderstood that the drawings is for the purpose of illustration anddescription and is not intended as a definition of the limits of theinvention. These and other objects attained, and advantages offered, bythe present invention will become more fully apparent as the descriptionthat now follows is read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Above-mentioned and other features and advantages of the presentinvention will be apparent from the following detailed description ofpreferred embodiments, merely exemplifying, in conjunction with theattached drawing, wherein:

FIG. 1 is a schematic view of a generic telecommunication system inwhich the present invention can be employed;

FIG. 2 is a schematic diagram showing the steps performed during a VoIPservice data transmission using a HSDPA bearer;

FIG. 3 is a schematic diagram illustrating a probability densityfunction of mobile users of a communication system, where user densityis plotted as a function of mobility;

FIG. 4 a is a schematic diagram showing the steps performed inaccordance with main principles of the present invention;

FIG. 4 b is a schematic diagram showing the steps performed inaccordance with an embodiment of the present invention;

FIG. 5 is a schematic diagram illustrating a probability densityfunction of mobile users of a communication system and a schedulingcondition implemented as a mobility threshold, where user density isplotted as a function of mobility; and

FIG. 6 is an example embodiment of a radio network controller accordingto the present invention.

FIG. 7 is a first embodiment of an user equipment according to thepresent invention.

FIG. 8 is a second embodiment of an user equipment according to thepresent invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth such as particulararchitectures, interfaces, techniques, etc. in order to provide athorough understanding of the present invention. However, it will beapparent to those skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.In other instances, detailed descriptions of well-known devices,circuits, and methods are omitted so as not to obscure the descriptionof the present invention with unnecessary details. Moreover, individualfunction blocks are shown in some of the figures. Those skilled in theart will appreciate that the functions may be implemented usingindividual hardware circuits, using software functioning in conjunctionwith a suitably programmed digital microprocessor or general purposecomputer, using an application specific integrated circuit (ASIC),and/or using one or more digital signal processors (DSPs).

It should be noted that, even if the description hereinafter mainly isdirected at a UMTS system and data bearer in such a system, theinvention is applicable in a CDMA2000 system and on data bearers forsuch a system to reduce the impact of the handover on speech quality inCDMA2000 using HDR (High Data Rate) and, hence, enhance the perceivedinteractivity in user communications. A HDR system is optimized forpacket data services, with a flexible architecture based on IPprotocols. HDR can overlay an existing wireless network or work as astand-alone system. HDR, known as TIA/EIA/IS-856 “CDMA2000, High RatePacket Data Air Interface Specification” is also known as 1×EV.

Moreover, the invention is applicable in communication between an userequipment in a UMTS system or in a CDMA2000 system and other userequipments, PSTN phones, etc.

FIG. 1 illustrates a generic telecommunications system as an examplecontext in which the present invention may be employed. The firstexample system includes both a radio access network 10 and a corenetwork 14. The core network 14 is shown as being connected to a servicenode or service network 16. The service network 16 (or other comparableentity) includes an application server 18, such as a, for example, aSIP-based PoC Server.

In one specific example implementation, the core network 14 is aconnectionless external core network and comprises Serving GPRS SupportNode (SGSN) 20 and Gateway GRPS support node (GGSN) 21. The GeneralPacket Radio Service (GPRS) Service (SGSN) node 20 is tailored toprovide packet-switched type services. The Gateway GRPS support node(GGSN) 21 provides the interface towards the packet-switched networks(e.g., the Internet, X.25 external networks). The Gateway GRPS supportnode (GGSN) 21 translates data formats, signalling protocols and addressinformation in order to permit communication between the differentnetworks. Serving GPRS Support Node (SGSN) 20 provides packet routing toand from a SGSN service area, and serves GPRS subscribers which arephysically located within the SGSN service area. Serving GPRS SupportNode (SGSN) 20 provides functions such as authentication, ciphering,mobility management, charging data, and logical link management towardthe user equipment unit. A GPRS subscriber may be served by any SGSN inthe network depending on location. The functionality of Serving GPRSSupport Node (SGSN) 20 and Gateway GRPS support node (GGSN) 21 may becombined in the same node, or may exist in separate nodes as shown inFIG. 1.

The core network 14 connects to radio access network 10 over a radioaccess network interface depicted by dot-dashed line 22. The radioaccess network 10 includes one or more control nodes 26 and one or moreradio base stations (BS) 28. In an example, non-limiting implementationin which radio access network 10 is a UMTS Terrestrial Radio AccessNetwork (UTRAN), the radio access network interface depicted bydot-dashed line 22 is known as the Iu interface, and the control nodes26 take the form of radio network controllers (RNCs). In otherimplementations of radio access network 10, the control nodes 26 canhave other names, such as base station controller (BSC), for example. Inany event, it should be understood that, for sake of simplicity, theradio access network 10 of FIG. 1 is shown with only one control node26, with the control node 26 being connected to two base stations (BS)28. As understood by those skilled in the art, the radio access network10 typically has numerous control nodes 26, which can be connected overan unillustrated interface (such as an Iur interface). Again for sake ofsimplicity, only two base station nodes 28 are shown connected to therepresentative control node 26. It will be appreciated that a differentnumber of base stations 28 can be served by each control node 26, andthat control nodes 26 need not serve the same number of base stations.Further, those skilled in the art will also appreciate that a basestation is sometimes also referred to in the art as a radio basestation, a node B, or B-node.

For brevity it is assumed in the ensuing discussion that each basestation 28 serves one cell. It will be appreciated by those skilled inthe art, however, that a base station may serve for communicating acrossthe air interface for more than one cell. For example, two cells mayutilize resources situated at the same base station site. Moreover, eachcell may be divided into one or more sectors, with each sector havingone or more cell/carriers.

A wireless terminal 30 communicates with one or more cells or one ormore base stations (BS) 28 over a radio or air interface 32. Indiffering implementations, the wireless terminal 30 can be known bydifferent names, such as mobile station or MS, mobile terminal or MT, oruser equipment unit (UE), for example. Of course, whereas for ease ofillustration only one wireless terminal 30 is shown in FIG. 1, each basestation typically serves many wireless terminals.

In the example UMTS implementation mentioned above, radio access ispreferably based upon Wideband, Code Division Multiple Access (WCDMA)with individual radio channels allocated using CDMA spreading codes. Ofcourse, other access methods may be employed.

In such a W-CDMA communication system in conformity with 3GPP (3^(rd)Generation Partnership Project) now being standardized, HSDPA may beused to realize high-speed downlink. In a HSDPA method, as a physicalchannel for a downlink through which data are transmitted from a basestation to a user equipment, an HS-SCCH (High Speed-Shared ControlCHannel) and an HS-PDSCH (High Speed-Physical Downlink Shared CHannel)are additionally provided. The HS-SCCH is used to transmit controlinformation of the HS-PDSCH pairing up with HS-SCCH, while the HS-PDSCHis used to transmit packet data employed in the HSDPA method. Inaddition, the communication system supports the use of traditionaldedicated channels (DCH).

It is believed that the system capacity can be significantly increasedwith HSPA in comparison to DCH, approximately the capacity increaseusing HSPA can be as large as 100 percent. However, a problem with HSDPAis, as outlined above, that it does not support soft handover. This incontrast to DHC bearers, which support soft handovers that do not leadto packet loss. The effect of packet loss is that handovers betweencells is experienced as interruptions in the speech communication. Ifthe handovers occur frequently, this may be very annoying and may,hence, have an negative impact on the perceived interactivity in theuser communications. Radio network simulations have shown that thecurrent delay in the transmission may be can be as long as 160 ms oreven longer. This delay time depends, for example, strongly on the uservelocity in that users with a high velocity encounter handoverinterruptions that are longer and occur more frequently.

With reference now to FIG. 2, the steps involved in communication over aHSPA bearer between users of user equipments using a VoIP service, suchas a MMTel service or a PoC service will be described. It should benoted that this is only an example and there are of course otherservices that may be communicated over a HSPA bearer and thus mayencounter interruptions due to soft handover. In this example, for thesake of simplicity, only two users are discussed but the skilled man inthe art realizes that the services can be used for communication betweenone user and an arbitrary number of users. User A wishes to communicatea message to user B. First, at step 100, user A accesses the desiredVoIP service, for example, by pressing a VoIP service button on his userequipment or VoIP service client, for example, a mobile phone. Then, atstep 102, the VoIP service client sends a request to the applicationserver 18, see FIG. 1, asking for permission to generate data to besent. Subsequently, at step 104, the application server decides if itshould grant or reject the request and sends either an accept signal ora reject signal back to client A. Upon receiving the accept signal, atstep 106, client A is arranged to indicate for User A that he or she isallowed to generate the signals to be sent. The indication may, forexample, be a visual or audible signal. The signal is encoded andordered in packets before transmission. Thereafter, the packets, fromclient A, are transmitted over the air interface 22, to the base station28 of the cell in which the user B is in. The radio network controller26 governing the base station 28 schedules, at step 108, thetransmission of the packets to a HSDPA bearer for the downlink trafficto user B. Then, at step 110, client B starts, upon receiving thepackets, the decoder processing of the received speech frames of thereceived packets and the decoded speech frames are played out to User Bby the loudspeaker in client B.

As discussed above, as HSDPA does not support soft handover,interruptions of the data traffic in the downlink may occur depending onthe travelling velocity of user B. These interruptions will be morecommon and will have a longer duration the higher the travellingvelocity of user B becomes since the handover frequency, or themobility, increases. The probability density function of the mobileusers in a system, for example, the system 10 in FIG. 1 may look likeFIG. 3 in which the user density as a function of mobility isillustrated. As can be seen, there is a large number of users that aremore or less stationary or travelling at a low velocity, e.g. walking.These user will likely not be affected of interruptions due to softhandover since they probably not will travel from one cell to anotherand if they do so, it will occur seldom. Hence, the potential orpossible interruptions will not be too annoying for these users. On theother hand, there is also a large number of users travelling at arelatively high speed by, for example, car or train, which entails thatthe mobility of these user will be high. These users will encounterinterruptions due to packet loss in the speech communication on afrequent basis. The interruptions may be as long as 160 ms or, incertain cases, even longer. In fact, it may be up to 500 ms. This may beexperienced as very annoying if the interruptions occur often.

The invention is based on that the individual VoIP services arescheduled to use either HSPA or DCH depending on the mobility of theusers. Users who experience a high handover frequency are scheduled touse DCH bearers, while users, in the low handover frequency case, willbe scheduled to use HSPA bearers. However, as mentioned above, theinvention is equally applicable in a CDMA2000 system for data bearers insuch a system.

Turning now to FIG. 4 a, the main principles of the method according tothe present invention will be described. The method for scheduling adata transmission to a user equipment arranged to communicate with atleast a second user using, for example, a second equipment or a PSTNphone may be implemented in a communication system as described withreference to FIG. 1. The scheduling of the usage of either HSDPA or DCHbearers can be performed according to following principle methods:

-   -   1. Session Description Protocol (SDP) setup: The decision is        made at session setup. The mobility of a specific UE may be        stored in a RNC or the UE may report the mobility at setup.    -   2. Dynamic allocation: The scheduling (HSDPA or DCH) is        performed during the session.

According to an embodiment of the present invention, the following stepsare performed in order to schedule a data transmission, for example, aVoIP service. In general, the steps involved in communication over adata bearer between users of user equipments using a VoIP service, suchas a MMTel service, a PoC service or a PoC VGM (Video Group Message)service is performed in accordance with the steps 100-106 described withreference to FIG. 2.

Now, the steps specific for the present invention will be described. Forexample, the following steps may be performed as an alternative to step108 or at SDP setup. First, at step 200, at least one predeterminedscheduling condition for data transmissions to a receiving UE isidentified. This step may be performed at setup. Preferably, this atleast one condition comprises the mobility of the UE and can beimplemented as a mobility threshold as shown in FIG. 5. Preferably, aHSDPA bearer is selected if an current mobility of the receiving UE isdetermined to be below the threshold and a DCH bearer is selected if thecurrent mobility is determined to be above the threshold. In oneembodiment of the present invention, the threshold is adjustable, asindicated in FIG. 5. Thereby, the threshold can be adjusted depending onsystem load and/or operator preferences. For example, if the system loadis very high, it may be desirable to move the threshold to a very highmobility value, as indicated by reference numeral 320, in order tomaximize the system capacity even though the HSPA handovers may becomeannoying. If the load is low, the threshold may be moved to a low value,as indicated by reference numeral 330. Then, at step 202, at least onecurrent scheduling condition of the UE is determined, which preferablyincludes determining the current mobility of the UE. This may beperformed at set up and the mobility of the specific UE may be stored inthe RNC or the UE may report the mobility at setup. Alternatively, thiscan be performed continuously, i.e. dynamic allocation. Thereafter, atstep 204, the predetermined scheduling conditions of the UE is comparedwith the current conditions of the UE, i.e. the predetermined mobilitythreshold is compared with the current mobility of the UE. Subsequently,at step 206, a high speed packet access (HSPA) bearer or a dedicatedchannel (DHC) for the data transmissions during the session based on thecomparison is selected. A HSDPA bearer is selected if the currentmobility of the receiving UE is determined to be below the predeterminedthreshold and a DCH bearer is selected if the current mobility isdetermined to be above the threshold. At step 208, the selected databearer is used during the data transmission session or until a new databearer has been selected if the allocation is dynamic. In an alternativeembodiment of the present invention, all steps are performed in thescheduling step 108 described with reference to FIG. 2.

The mobility of users can be devised in number of ways. A first way isto determine the handover frequency of the UE, i.e. the number ofhandovers per time unit. Another way is to determine a Doppler shift ofthe carrier frequency, which gives an estimate of the UE speed withrespect to one or several base stations. A third way is to usepositioning data, for example, by means of a GPS receiver in the UE, todetermine a velocity relatively one or several base stations.

According to an embodiment, the scheduling conditions also include thetype of traffic flow. In this case, the scheduling can be executed inthe following way. If for instance the traffic flow is non realtimewebtraffic it is possible that an UE is allowed to use HSDPA bearerseven though the mobility is above the threshold. If the traffic flow islow latency streaming video or audio, or even VoIP, it is likely thatthe number of handovers become annoying and that may therefore be betterto allocate DCH bearers for this traffic flow. Other conditions that canbe used is, for example, Quality of Service (QoS).

With reference to FIG. 4 b, an embodiment of the present invention willbe described. The method for scheduling a data transmission to a userequipment in a communication system as described with reference toFIG. 1. As mentioned above, the scheduling of the usage of either HSDPAor DCH bearers can be performed dynamically and the following steps areperformed in order to schedule a data transmission, for example, a VoIPservice. In general, the steps involved in communication over a databearer between users of user equipments using a VoIP service, such as aPoC service or a PoC VGM (Video Group Message) service is performed inaccordance with the steps 100-106 described with reference to FIG. 2.

Now, the steps specific for an embodiment realizing a dynamic approachwill be described. First, at step 220, at least one predeterminedscheduling condition for data transmissions to a receiving UE isidentified. This step may be performed at setup. Preferably, this atleast one condition comprises the mobility of the UE and can beimplemented as a mobility threshold as shown in FIG. 5. Preferably, aHSDPA bearer is selected if an current mobility of the receiving UE isdetermined to be below the threshold and a DCH bearer is selected if thecurrent mobility is determined to be above the threshold. In oneembodiment of the present invention, the threshold is adjustable, asindicated in FIG. 5. Thereby, the threshold can be adjusted depending onsystem load and/or operator preferences. For example, if the system loadis very high, it may be desirable to move the threshold to a very highmobility value, as indicated by reference numeral 320, in order tomaximize the system capacity even though the HSPA handovers may becomeannoying. If the load is low, the threshold may be moved to a low value,as indicated by reference numeral 330. Then, at step 222, at least onecurrent scheduling condition of the UE is determined, which preferablyincludes determining the current mobility of the UE. Thereafter, at step224, the predetermined scheduling conditions of the UE is compared withthe current conditions of the UE, i.e. the predetermined mobilitythreshold is compared with the current mobility of the UE. Subsequently,at step 226, a high speed packet access (HSPA) bearer or a dedicatedchannel (DHC) for the data transmissions during the session based on thecomparison is selected. A HSDPA bearer is selected if the currentmobility of the receiving UE is determined to be below the predeterminedthreshold and a DCH bearer is selected if the current mobility isdetermined to be above the threshold. At step 228, the selected databearer is used during the data transmission session or until a new databearer has been selected. In an alternative embodiment of the presentinvention, all steps are performed in the scheduling step 108 describedwith reference to FIG. 2. At step 230 the current conditions of the userequipment are checked continuously during the session and it checkedwhether the current conditions has changed. If the conditions haschanged, in step 232, the updated conditions are compared with thepredetermined scheduling conditions and it is checked whether theselected data bearer should be changed. That is, if the current mobilityof the UE has, for example, increased such that it exceeds thepredetermined threshold thus indicating that the data bearer should bechanged from a HSDPA bearer to a DCH bearer. Then, in step 234, the newdata bearer for the data transmissions based on the comparison betweenthe updated conditions with the predetermined scheduling conditions isselected. The procedure then return to step 230.

Turning now to FIG. 6, an example RNC according to the present inventionwill be described. As briefly mentioned above, the main functions of theRNC are management of radio channels on the interfaces between UE andnode-B (base station) Uu. Radio resource management includes thefollowing: outer loop power control, load control, admission control,packet scheduling, handover control, security functions and mobilitymanagement. According to an embodiment, the radio network controller(RNC) 400 governing a number of base stations 402 in a communicationsystem (for example the system in FIG. 1), wherein the communicationsystem supports data transmission from a base station to an userequipment on a high speed packet access (HSPA) bearer or a dedicatedchannel (DHC), is adapted to schedule data transmissions to an UE 404arranged to communicate with at least a second UE 404. The RNC 400comprises: identifying means 406 adapted to identify at least onepredetermined scheduling condition for data transmissions to the UE 404;determining means 408 adapted to determine at least one currentscheduling condition of the UE 404; comparator means 410 adapted tocompare the predetermined scheduling conditions of the UE 404 with thecurrent conditions of the UE 404; scheduling selecting means 412 adaptedto select a high speed packet access (HSPA) bearer or a dedicatedchannel (DHC) for the data transmissions during a session from a basestation based on the comparison, wherein the selected data bearer isused during the data transmission session or until a new data bearer hasbeen selected.

With reference to FIGS. 7 and 8, embodiments of the present invention auser equipment for use in a communication system comprising at least oneradio network controller (RNC) according to the invention, for example,the system and RNC described above governing a number of base stations,wherein the communication system supports data transmission from a basestation to an user equipment on a high speed packet access (HSPA) beareror a dedicated channel (DHC) or on similar bearers in a CDMA2000 systemwill be described. The function and parts of a user equipment for use ina UMTS or CDMA200 system are well known for the man skilled in the artand therefore description of these will be omitted and only partrelevant for the invention will be described. The user equipment 504comprises identifying means 508 adapted to identify at least onepredetermined scheduling condition for data transmissions for the userequipment; determining means 510 adapted to determine at least onecurrent scheduling condition of the user equipment; comparing means 512adapted to compare the predetermined scheduling conditions of the userequipment with the current conditions of the user equipment; and meansfor communicating 514 the comparison to the RNC.

In an alternative embodiment, the user equipment 604 comprisesdetermining means 610 adapted to determine at least one currentscheduling condition of the user equipment; and means for communicating614 the at least one current scheduling condition of the user equipmentto the RNC.

Although specific embodiments have been shown and described herein forpurposes of illustration and exemplification, it is understood by thoseof ordinary skill in the art that the specific embodiments shown anddescribed may be substituted for a wide variety of alternative and/orequivalent implementations without departing from the scope of theinvention. Those of ordinary skill in the art will readily appreciatethat the present invention could be implemented in a wide variety ofembodiments, including hardware and software implementations, orcombinations thereof. As an example, many of the functions describedabove may be obtained and carried out by suitable software comprised ina micro-chip or the like data carrier. This application is intended tocover any adaptations or variations of the preferred embodimentsdiscussed herein. Consequently, the present invention is defined by thewording of the appended claims and equivalents thereof and the inventionis not to be regarded as limited to only the structural or functionalelement described in the embodiments, but to the attached claims.

1. Method for scheduling a data transmission to a user equipment in acommunication system comprising at least one radio network controller(RNC) governing a number of base stations, wherein the communicationsystem supports data transmission from a base station to a userequipment on a high speed packet access (HSPA) bearer or a dedicatedchannel (DCH), said method comprising the steps of: identifying at leastone predetermined scheduling condition for data transmissions for saiduser equipment; determining at least one current scheduling conditionsof said user equipment; comparing said predetermined schedulingconditions of said user equipment with said current conditions of saiduser equipment; selecting a high speed packet access (HSPA) bearer or adedicated channel (DCH) for the data transmissions during a session froma base station based on said comparison; and using said selected databearer during the data transmission session or until a new data bearerhas been selected.
 2. The method according to claim 1, wherein said atleast one predetermined scheduling condition is a mobility threshold ofsaid user equipment and wherein said step of determining the currentscheduling conditions of said user equipment comprises the step ofdetermining the mobility of said user equipment and wherein a HSDPAbearer is selected if an current mobility of said user equipment isdetermined to be below said threshold and a DCH bearer is selected ifsaid current mobility is determined to be above said threshold.
 3. Themethod according to claim 1, wherein said mobility threshold is anadjustable mobility threshold.
 4. The method according to claim 1,further comprising the steps of: continuously checking said currentconditions of said user equipment during said session in order toidentify whether said current conditions has changed; if said conditionshas changed, comparing said updated conditions with said predeterminedscheduling conditions; if said comparison between said updatedconditions and said predetermined scheduling conditions indicates thatthe selected data bearer should be changed; selecting a new data bearerfor the data transmissions based on said comparison between said updatedconditions with said predetermined scheduling conditions; and using saidnew data bearer for data transmission.
 5. The method according to claim1, wherein said step of identifying predetermined scheduling conditionsfor data transmissions for said user equipment is performed at sessiondescription protocol setup.
 6. The method according to claim 1, whereinthe step of determining current scheduling conditions of said userequipment is performed at session description protocol setup.
 7. Themethod according to claim 6, further comprising the step of: collectingscheduling condition information for said user equipment in order todetermine current scheduling conditions for said user equipment.
 8. Themethod according to claim 7, wherein said scheduling information iscollected from said user equipment or from said radio networkcontroller.
 9. The method according to claim 2, wherein said step ofdetermining the mobility of said user equipment comprises the step ofdetermining a number of handovers per time unit for said user equipment.10. The method according to claim 2, wherein the step of determining themobility of said user equipment comprises the step of: calculating aDoppler shift of a carrier frequency of said user equipment in order toestimate a speed of said user equipment with respect of one ore severalbase stations.
 11. The method according to claim 2, wherein the step ofdetermining the mobility of said user equipment comprises the step of:determining a position of said user equipment at regular intervals usinga position system.
 12. The method according to claim 1, wherein saidscheduling conditions includes a traffic flow parameter.
 13. The methodaccording to claim 12, further comprising the step of checking the typeof traffic flow in said session.
 14. The method according to claim 12,wherein a HSDPA bearer or a similar bearer in a CDMA2000 system isselected if said traffic flow parameter indicates that time sensitivedata, including video, audio or VoIP, is transmitted in said session anda DCH bearer or a similar bearers in a CDMA2000 system is selected ifsaid traffic flow parameter indicates that non time sensitive trafficincluding non real-time traffic is transmitted in said session.
 15. Aradio network controller (RNC) in a communication system governing anumber of base stations, wherein the communication system supports datatransmission from a base station to an user equipment on a high speedpacket access (HSPA) bearer or a dedicated channel (DCH), said RNC beingadapted to schedule data transmissions to a user equipment in saidnetwork, wherein said radio network controller comprises: identifyingmeans adapted to identify at least one predetermined schedulingcondition for data transmissions for said user equipment; determiningmeans adapted to determine at least one current scheduling condition ofsaid user equipment; comparator means adapted to compare saidpredetermined scheduling conditions of said user equipment with saidcurrent conditions of said user equipment; scheduling selecting meansadapted to select a high speed packet access (HSPA) bearer or adedicated channel (DCH) for the data transmissions during a session froma base station based on said comparison, wherein said selected databearer is used during the data transmission session or until a new databearer has been selected.
 16. A mobile communication system comprisingat least one radio network controller (RNC) governing a number of basestations, wherein the communication system supports data transmissionfrom a base station to an user equipment on a high speed packet access(HSPA) bearer or a dedicated channel (DCH), said RNC being adapted toschedule a user equipment (404) in a data transmission in said network,wherein said radio network controller (RNC) is adapted to identify atleast one predetermined scheduling condition for data transmissions forsaid user equipment; determine at least one current schedulingconditions of said user equipment; compare said predetermined schedulingconditions of said user equipment with said current conditions of saiduser equipment; select a high speed packet access (HSPA) bearer or adedicated channel (DCH) for the data transmissions during a session froma base station based on said comparison; and use said selected databearer during the data transmission session or until a new data bearerhas been selected.
 17. A user equipment adapted to be scheduled by aradio network controller (RNC) in a mobile communication systemaccording to claim 16, said radio network controller (RNC) governing anumber of base stations, wherein the communication system supports datatransmission from a base station to said user equipment on a high speedpacket access (HSPA) bearer or a dedicated channel (DCH), the userequipment comprising identifying means adapted to identify at least onepredetermined scheduling condition for data transmissions for said userequipment; determining means adapted to determine at least one currentscheduling condition of said user equipment; comparing means adapted tocompare said predetermined scheduling conditions of said user equipmentwith said current conditions of said user equipment; and means forcommunicating said comparison to said radio network controller RNC, forthe RNC to select a high speed packet access (HSPA) bearer or adedicated channel (DCH) for the data transmissions during a session froma base station based on said comparison.
 18. The user equipmentaccording to claim 17, wherein said at least one predeterminedscheduling condition is a mobility threshold of said user equipment andwherein user equipment comprises means for determining the mobility ofsaid user equipment.
 19. The user equipment according to claim 17,wherein said mobility threshold is an adjustable mobility threshold. 20.The user equipment according to claim 17, further comprising: means forcontinuously checking said current conditions of said user equipmentduring said session in order to identify whether said current conditionshas changed; and wherein said comparing means is adapted to, if saidconditions has changed, compare said updated conditions with saidpredetermined scheduling conditions.
 21. The user equipment according toclaim 17, wherein the predetermined scheduling conditions for datatransmissions for said user equipment is identified at sessiondescription protocol setup.
 22. The user equipment according to claim17, wherein the current scheduling conditions of said user equipment isdetermined at session description protocol setup.
 23. The user equipmentaccording to claim 17, wherein said determining means is adapted todetermine the mobility of said user equipment by determining a number ofhandovers per time unit for said user equipment.
 24. The user equipmentaccording to claim 17, wherein said determining means is adapted todetermine the mobility of said user equipment by calculating a Dopplershift of a carrier frequency of said user equipment in order to estimatea speed of said user equipment with respect of one ore several basestations.
 25. The user equipment according to claim 17, furthercomprising a GPS receiver and wherein said determining means is adaptedto determine the mobility of said user equipment by determining aposition of said user equipment at regular intervals using positioninginformation obtained from a position system via said GPS receiver. 26.The user equipment according to claim 17, wherein said schedulingconditions includes a traffic flow parameter.
 27. The user equipmentaccording to claim 26, wherein said determining means is adapted tocheck the type of traffic flow in said session.
 28. A computer readablemedium comprising instructions for bringing a programmable device toperform steps of the method according claim 1